which one is better ?

and do the extra lvls of both only increase duation fot he shout?

As far as I can tell, Slow Time is absolutely useless, as it slows you down as well.

Slow time gives u more time to react and gives u more time to aim while under pressure.
Slow time or "bullet time" slows you down in other games too. See Max Payne or Fear for example, wasnt useless there either.
Nevertheless I dont find it very usefeul compared to other shouts that actually help u kill the enemy.

slow time helps you avoid being nuked and arrowed to death. if you are an archer its not really nessasary tho as you get it as a perk. if you are a dual weilder the elemental is better for you... tho i still feel enchanted weapons are just better. Elemental fury has too much downtime and requires an unenchanting weapon.. not to mention you have to shout to keep it up.

i think the superspeed sprint is the best choice all around.

I rarely, if ever use them, but elemental fury cannot be used on enchanted weapons so I would have to go with slow time.

I guess you guys have a point about Slow Time. Still, despite that reasoning, I've never found myself in a situation that it was more useful in combat than (m?)any of my other shouts. I never really find myself needing a heightened reaction time.

Is Elemental Fury usable with bound weapons? If so, It would probably see maximum potential there, with the Mystic Binding perk.

I feel that i do move faster with slow time example;
Im surrounded by Drugar with half hp so kite them into a cluster slow time and sweep attack them with my 2hander like 3 times before they finish landing their blows i move back switch to dual ice storm and finish them off as time comes back. Slow time kicks ass, screw elemental furry

I was very disappointed when I saw that I was as slowed as the enemies.

Max payne and fear are shooters. Beeing able to aim in time bullet in a shooter is well worth it. Skyrim is not the same.

Yes you're right, and I see no point in using it with a melee char either.
It would be very useful with a bow char, but thats exactly why marksmen have it as a perk already.
Only character it would make sense on is a destruction mage. So its not very useful.

Btw it does give me the impression that Im slowed only half as much as the enemies.